The present invention relates generally to the field of photolithography, and more particularly to micro-fabrication processes.
Electronic circuit simulation uses mathematical models to replicate the behavior of an actual electronic device or circuit. For integrated circuit (IC) design, electronic design automation (EDA) tools are often used. Simulation software allows for modeling of circuit operation and is an invaluable analysis tool. Simulating a circuit's behavior before actually building it improves design efficiency by revealing faulty designs and providing insight into the behavior of electronic circuit designs. In particular, for integrated circuits, the tooling (photomask) is expensive, breadboards are impractical, and probing the behavior of internal signals is difficult. Therefore, almost all IC design activities rely on circuit simulation.
Photolithography, also known as optical lithography, or UV lithography, is a process used in micro-fabrication to pattern parts of a thin film, or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical “photoresist” on the substrate.
Mask data preparation (MDP) is the procedure of translating a file containing the intended set of polygons from an integrated circuit layout into set of instructions that a photomask writer can use to generate a physical mask. MDP usually involves mask fracturing where complex polygons are translated into simpler shapes, often rectangles and trapezoids, that can be handled by the mask writing hardware. Recent MDP procedures require the additional steps of resolution enhancement technologies (RET) and/or optical proximity correction (OPC) with a focus on design for manufacturability.
Optical proximity correction (OPC) is a photolithography enhancement technique commonly used to compensate for image errors due to diffraction, or process effects. The need for OPC often arises in the making of semiconductor devices due to the limitations of light to maintain the edge placement integrity of the original design, after processing, into the etched image on the silicon wafer.
OPC and verification model accuracy depend on having a large number of data points for calibration. The requirement of a large number of data points drives up process costs, but the results are precise. For example, OPC models use optics (physical) and empirical resist models to balance the accuracy and speed of processing, which leads to a high dependency on the amount of data collected, the relevance of the data to all design constructs that are going to be placed on the mask, the precision of metrology, and the SEM (scanning electron microscopy) offsets to physical data. Conventional manufacturability efforts, such as OPC are confronted with the negative effects associated with the enormous amounts of data they can produce (too much data can sometimes become a problem for the mask writer to be able to create a mask in a reasonable amount of time).
Contour tracing, also known as border following or boundary following, is a technique that is applied to digital images in order to extract their boundary (referred to herein as “contour extraction.” Once the contour of a given pattern is extracted, its characteristics may be examined and used as features for use in pattern classification. It is known to extract and encode the boundary points of contours.